Throttle apparatus for an internal combustion engine

ABSTRACT

A returning spring  7  of the electronic control throttle and a default spring  8  for securing an initial opening degree (default opening degree) of the throttle valve  3  have diameters different from each other, and both of the springs  7, 8  are held around a shaft of the throttle valve shaft  3  and arranged between a gear  43  attached to the throttle valve shaft  3  and a wall portion of the throttle body  100.  A shaft supporting gap of the throttle valve shaft  3  is filled with an air leak preventing material, and a minimum opening degree on control purpose of the throttle valve is set to a value larger than an amount of overshoot of the throttle valve occurring when opening degree of the throttle valve is changed from a maximum opening degree on control purpose of the throttle valve to the minimum opening degree.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a throttle apparatus for aninternal combustion engine and, more particularly, to an electroniccontrol throttle device which controls opening and closing a throttlevalve by driving an electric driven actuator based on a control signal.

[0002] In the electronic control throttle apparatus for controlling athrottle valve of an engine by driving an electric driven actuator (forexample, a direct current motor, a stepping motor), a technology knownis that an initial opening degree (default opening degree) of thethrottle valve in an off state of engine key (in other words, at notenergized state of the electric driven actuator) is set to a positionlarger than its full close position.

[0003] Here, the full close position does not mean a position forcompletely choking the intake air passage. Particularly, in a throttledevice performing idling rotating speed control using only a throttlevalve without any bypass passage for bypassing the throttle valve, thefull close position is defined by classifying into a mechanical fullclose position and an electrical full close position to be describedbelow.

[0004] The mechanical full close position means a minimum opening degreeposition of a throttle valve determined by a stopper, and the minimumopening degree is set at a position to slightly open the throttle valvefrom a position to completely choking the intake air passage in order toprevent the throttle valve from sticking. The electrical full closeposition means a minimum opening degree within a range of openingdegrees used for control, and the minimum opening degree is set at anopening position slightly larger than the mechanical full close positionin taking the mechanical full close position as the reference bycontrolling of driving the electric driven actuator (for instance, aposition larger than the mechanical full close position by approximately1°). In the electronic control throttle device, the electrical fullclose position (the minimum opening degree on the control purpose) doesnot always agree with an idling opening degree (an opening degreenecessary for idling rotating speed control). The reason is that becausethe opening degree of the throttle valve is feedback controlled based onan idling rotating speed detected signal in order to keep the idlingrotating speed to a target rotating speed, and thereby the openingdegree can not be determined uniquely.

[0005] In regard to a full open position, there are a mechanical fullopen position determined by a stopper and an electrical full openposition of a maximum opening degree on control. Therein, in a case ofsimply describing a “full close position”, meaning of the word includesthe electrical full close position as well as the mechanical full closeposition. In a normal control, the throttle valve is controlled betweenthe electrical full close position (the minimum opening degree on thecontrol purpose) and the electrical full open position (the maximumopening degree on the control purpose). By doing so, a part of thethrottle valve does not hit on the stoppers for determining themechanical full close position and the mechanical full open position atcontrolling the throttle valve to the minimum and the maximum openingdegrees. Therefore, mechanical fatigue, abrasion and damage of thestoppers and the gear members can be prevented and sticking of thethrottle valve to the stopper can be prevented.

[0006] A default opening degree (that is, the initial opening degree inan off state of engine key) is set to an opening degree of a position inwhich the throttle valve is further opened wider than that in the fullclose position (the mechanical full close position and the electricalfull close position)(for example, a position larger than the mechanicalfull close position by 4 to 13°). One reason why the default openingdegree is set is that an air flow rate necessary for combustion ofpre-warming-up operation at stating -up of the engine (cold starting-up)is secured without any auxiliary air passage (an air passage bypassingthe throttle valve). During idling operation, as the engine is warmedup, the throttle valve is controlled so as to moved from the defaultopening degree toward the smaller opening degree. However, the lowerlimit is the electrical full close position. Another reason why thedefault opening degree is set is to cope with requirements for securingself-running (limp home) or for securing an intake air flow rate toprevent the engine operation from stopping even if the throttle controlsystem is failed, for preventing the throttle valve from fixing to aninner surface of the throttle body with a viscous substance or ice.

[0007] As conventional examples of default opening degree settingmechanisms, various kinds of default opening degree setting mechanismsare proposed in, for example, Japanese Patent Application Laid-OpenNo.63-150449, U.S. Pat. No. 4,947,815 and the corresponding patent ofJapanese Patent Application Laid-Open No.2-500677, Japanese PatentApplication Laid-Open No.62-82238 and the corresponding patent of U.S.Pat. No. 4,735,179 by the same applicant of the present invention,Japanese Patent Application Laid-Open No.10-89096, Japanese PatentApplication Laid-Open No.10-131771 and so on.

[0008] There are various types of default opening degree settingmechanisms. For example, one type is that a default opening degree issecured by setting the relationship between forces of a returning springfor acting a force toward a closing direction of the throttle valve andan opposed spring (called as a default spring or an initial openingdegree spring) for acting a force toward an opening direction of thethrottle valve opposing against the force of the returning spring sothat the force of the default spring is larger than the force of thereturning spring at the default opening degree position and so that afree end of the default spring is stopped by a default stopper at thedefault opening degree position when the engine key is switched off (forexample, Japanese Patent Application Laid-Open No.2-500677).

[0009] Another type is, as disclosed in Japanese Patent ApplicationLaid-Open No.1-131771, that a fixing side engaging element to be fixedto a throttle valve shaft (this engaging element may be constructed by athrottle lever, or a gear for transmitting motor power may be usedinstead of the engaging element) and a moving side engaging element (alinking lever) idly inserted onto the throttle valve shaft and rotatablerelative to the throttle valve shaft are provided, and the moving sideengaging element and the fixing side engaging element are linkedtogether with a returning spring so as to attract each other, and aforce is applied using a default spring onto the moving side engagingelement in a direction of opening the throttle valve to engage androtate the moving side engaging element and the fixing side engagingelement (the throttle valve shaft) together opposing against the forceof the default spring when the opening degree is within the rangesmaller than the default opening degree (smaller than the defaultstopper position), and to rotate only the fixing side engaging elementand accordingly the throttle valve shaft opposing against the force ofthe returning spring and preventing movement of the moving side engagingelement by the default stopper when the opening degree is within therange larger than the default opening degree. On the contrary, there isa type that the moving side engaging element and the fixing sideengaging element are linked together with the default spring so as toattract each other, and a force is applied using the returning springonto the moving side engaging element in a direction of closing thethrottle valve to engage and rotate the moving side engaging element andthe fixing side engaging element (the throttle valve shaft) togetheropposing against the force of the returning spring when the openingdegree is within the range larger than the default opening degree, andto rotate only the fixing side engaging element (the throttle valveshaft) opposing against the force of the default spring and preventingmovement of the moving side engaging element by the default stopper whenthe opening degree is within the range smaller than the default openingdegree.

[0010] The electronic control throttle device can more accuratelyperform air flow rate control suitable for operation of an internalcombustion engine than a mechanical throttle device in which an amountof stepping-in of the accelerator pedal is transmitted to a throttlevalve shaft through an accelerator wire. However, since the electroniccontrol throttle device has the electric drive actuator and the defaultopening degree setting mechanism, number of the parts is increased andaccordingly it is important how to make the throttle body small in size,light in weight and simple in structure and how to simplify the wiring(wire harness).

[0011] Further, the electronic control throttle device controls theidling rotating speed by controlling opening degree of the throttlevalve, but has the following point to be improved.

[0012] In a case where idling rotating speed control is performed withthe throttle valve in the electronic control throttle device, an openingdegree larger than the mechanical full close position by a certain angle(for example, 5 to 1°) is secured at least as the minimum opening degreeon the control purpose. Since a gap (sometime called as a shaft supportgap) between the throttle valve shaft and a shaft inserting through holeprovided in a wall of the throttle body which guides the throttle valveshaft to a bearing practically serves as a part of the intake airpassage and the air flow rate (leak air flow rate) flowing through theshaft support gap can not be controlled, the minimum opening degree onthe control purpose is set with taking it into consideration that theleak flow rate flows into the internal combustion engine.

[0013] However, according to the conventional set value of the minimumopening degree for the control purpose (the electrical full closeposition), when the throttle valve is closed from the maximum openingdegree for the control purpose (the electrical full open position)toward the minimum opening degree (the electrical full close position,in the idling state), a magnitude of overshoot becomes larger than theminimum opening degree in the closing direction (the overshoot isapproximately 1.5° at maximum) because the driving force of the motor(the electric drive actuator) is decreased at high temperature or at lowtemperature (that is, the torque of the motor is reduced at hightemperature due to increase in the resistance of the motor, and thetorque of the motor is reduced at low temperature due to decease in thebattery voltage). As a result, as shown by a solid line {circle over(1)} in FIG. 17, the throttle valve hits on the stopper at themechanical full close position (the diagonally shaded area in FIG. 17indicates a state that movement of the throttle valve is blocked by thefull close stopper.), and over-current flows in the motor likely tocause an erroneous fail-safe diagnosis (an erroneous diagnosis judgingof occurrence of failure in the motor from the over current) or decreasein the lifetime of the motor.

SUMMARY OF THE INVENTION

[0014] An object of the present invention is to make an electroniccontrol throttle device having an electric drive actuator, a gearmechanism, a default opening degree setting mechanism small in size,light in weight and simple in assembling and wire harness by solving theabove-mentioned problems.

[0015] Another object of the present invention is to improve reliabilityof the electronic control throttle device by preventing the throttlevalve from hitting on the stopper even if such an overshoot as describedabove occurs in the throttle valve.

[0016] The present invention is basically constructed as follows.

[0017] A throttle device for an internal combustion engine according toone aspect of the present invention includes an electric drive actuatorand a default opening degree setting mechanism, wherein

[0018] a gear case for containing a gear mechanism to transmit power ofthe electric drive actuator to a throttle valve shaft is arranged on anouter wall of a throttle body, and

[0019] a returning spring for acting a spring force on the throttlevalve in a closing direction and a spring (a default spring) for actinga spring force on the throttle valve in a direction toward a side of thedefault opening degree seeing from the full close position of thethrottle valve have diameters different from each other, and both of thesprings are held around a shaft of said throttle valve shaft andarranged between a gear attached to the throttle valve shaft in the gearmechanism and a wall portion of the throttle body.

[0020] According to the above-mentioned construction, the returningspring and the default spring can be intensively arranged between thegear provided in the throttle shaft and the wall portion of the throttlebody, and accordingly the part space can be rationalized. Particularly,according to the present invention, by arranging the returning springand the default spring in such a feature that at least a part of thereturning spring and a part of the default spring are overlapped witheach other (one spring having a smaller diameter is inserted inside theother spring having a larger diameter), an arranging space in alongitudinal direction of the springs can be shortened, and accordinglythis structure is useful in that the gear case and the whole throttlebody can be made small in size, light in weight and simple inassembling.

[0021] In addition to the above-mentioned construction, the presentinvention proposes a construction that the spring arranged outside outof the returning spring and the default spring (the spring having thelarger diameter) is placed in being guided by an outer periphery of abearing containing boss for the throttle valve shaft projecting inwardof the gear case in a manner that one end of the spring having thelarger diameter is fixed to the wall portion of the throttle body. Bydoing so, the outer periphery of the bearing containing boss for thethrottle valve shaft can be used for a space placing one spring out ofthe returning spring and the default spring. Accordingly, this structureis useful in that the parts can be more intensively arranged, and thethrottle body can be made smaller in size and light in weight. Althoughthe other various dependent invention in regard to the first inventionare proposed, these will be described in the item of DESCRIPTION OF THEPREFERRED EMBODIMENTS later.

[0022] In an electronic control throttle device according to anotheraspect of the present invention, a throttle body, a motor casecontaining a motor composing an electric drive actuator and a containingportion of a connector connecting by plugging to a motor terminalprovided in an end plate of said motor are formed in a unit. Inaddition, a motor terminal extracting port for exposing the motorterminal to the containing portion of the connector is formed on abottom portion of the motor case, and a guide for guiding the connectorto the motor terminal extracting port when the connector is plugged tothe motor terminal is formed on an inner wall surface of the containingportion of the connector.

[0023] By constructing as described above, the connector can be easilyconnected to the motor terminal without difficulty of positioning theconnector to the motor terminal because by containing the motor in themotor case the motor terminal can be seen in the containing portion ofthe connector (the terminal connector) through the terminal extractingport, and in this state the terminal connector is inserted from theterminal containing portion using the guide. Even if the motor terminalis, particularly, placed in a deep position of the connector containingportion and behind the other parts, the connector can be inserted bybeing guided by the above-mentioned guide without difficulty while beingpositioned.

[0024] In an electronic control throttle device according to a furtheraspect of the present invention, a motor case for containing a motorcomposing the electric drive actuator is integrated with a throttle bodyin a unit. In addition, in the throttle body, a motor terminalextracting port is formed in a side of a bottom portion of the motorcase, a containing space of a connector to be connected to the motorterminal being formed adjacent to the side of the bottom portion of saidmotor case, the containing space of the connector and a containing spacefor containing a throttle sensor provided at one end of a throttle valveshaft being formed in one room, a wire lead portion of the throttlesensor being arranged in being directed to the containing space of themotor terminal connector.

[0025] By constructing as described above, the wires led from theterminal of the throttle sensor and the wires led from the motorterminal can be merged at adjacent positions in the beginning in theconnector and throttle sensor containing space (one room), andaccordingly these wires can be gathered without difficulty and can beextracted out of the throttle body. Therefore, this construction isuseful to simplify the wiring work and the part assembling work.

[0026] An electronic control throttle device according to a furtheraspect of the present invention, a motor case for containing a motorcomposing the electric drive actuator and a gear case for containing agear mechanism to transmit power of the motor to a throttle valve shaftare integrated in a unit. In addition, a motor inserting port of themotor case is opened to the gear case, the motor being attached to themotor case by fastening a motor bracket to triangular point arrangedscrew holes provided a periphery of the motor inserting port with threescrews in total, three sides forming a contour of the motor bracketbeing curved lines, a motor positioning portion fitting to the threecurved lines of the motor bracket to position the motor being formed inthe gear case.

[0027] By constructing as described above, vibration of the motor can besuppressed more effectively than in a conventional one in which themotor bracket is fastened at two points with screws, and furtheraccuracy of positioning the motor can be improved.

[0028] An electronic control throttle device according to a furtheraspect of the present invention includes an electric drive actuator foropening and closing a throttle valve based on a signal controlling anintake air flow rate of the internal combustion engine. In addition, agap (a shaft supporting gap) between a throttle valve shaft and a shaftinserting through hole for guiding the throttle valve shaft to a bearingprovided in a wall portion of a throttle body is filled with an air leakpreventing material, and a minimum opening degree on control purpose ofthe throttle valve is set to a value larger than an amount of overshootof the throttle valve occurring when opening degree of the throttlevalve is changed from a maximum opening degree on control purpose of thethrottle valve to the minimum opening degree.

[0029] By constructing as described above, since the intake air flowrate (the leak air flow rate) supplied to the internal combustion enginethrough the so-called shaft supporting gap of the throttle valve shaftcan be eliminated, the minimum opening degree on the control purpose ofthe throttle valve can be increased larger than in the conventional oneby that amount. In the present invention, by making use of this fact theminimum opening degree on the control purpose is set a value lager thanthe overshoot of the throttle valve when opening degree of the throttlevalve is changed from the maximum opening degree on control purpose ofthe throttle valve to the minimum opening degree. For instance, byapplying the air leak preventing material (for example, molybdenumdisulfide), as shown by the solid line {circle over (2)} in FIG. 17,since the minimum opening degree on the control purpose can be set avalue lager than the mechanical full close position by approximately 2°,the minimum opening degree on the control purpose can be increasedhigher by a value corresponding to the overshoot (for instance,approximately 1.5°) when opening degree of the throttle valve is changedfrom the maximum opening degree on control purpose (the electrical fullopen position) to the minimum opening degree (the electrical full closeposition). Therefore, the stopper blocking element in the side of thethrottle valve can be prevented from hitting on the stopper (the fullclose stopper) determining the mechanical full close position even ifthe overshoot occurs. Accordingly, even if the overshoot occurs, it ispossible to prevent over current from flowing in the motor.

[0030] The above-mentioned operation and effect are attained on thepremises that the gap (the shaft supporting gap) between the throttlevalve shaft and the shaft inserting through hole for guiding thethrottle valve shaft to the bearing provided in the wall portion of thethrottle body is filled with the air leak preventing material. Theabove-mentioned operation and effect can not be expected in a mechanicalthrottle device in which a stepping amount of an accelerator istransmitted to a throttle valve shaft through an accelerator wire evenif the so-called shaft supporting gap is filled with the air leakpreventing material. The reason is as follows. The idling opening degreein the mechanical throttle device is set to a position where amechanical full closing stopper exists, and the mechanical throttledevice is designed on the premises that the stopper blocking elementcontrolling the throttle valve hits on the full close stopper duringoperation. Further, since the throttle valve is mechanically drivenusing the accelerator wire, there is no occurrence of overshoot noroccurrence of over current attendant on the overshoot differently fromin the electronic control throttle device.

[0031] The Japanese Patent Application Laid-Open No.62-17100 proposes atechnology that in a mechanical throttle device, a dryable liquidlubricant (for example, molybdenum disulfide) is penetrated into an airpassage formed between a throttle valve shaft and a shaft insertingthrough hole in a wall portion of the throttle valve assembly (the shaftsupporting gap) and dried to fill the air passage with the lubricantsolidified and fixed to the air passage. On the background that anidling rotating speed of an engine is set in taking the amount of theair flowing through the so-called shaft supporting gap intoconsideration since the air flowing through the gap can not becontrolled by the throttle valve, but the idling rotating speed isgradually decreased and finally the engine may be stopped becausecombustion products (combustion soot, viscous substance or the like) aregradually accumulated in the shaft supporting gap. Therefore, thesetting of the idling rotating speed is performed by eliminating the gapin the beginning to eliminate the change in the idling air flow ratewith time and by using a full close stopper (an idling adjust screw).

[0032] In the electronic control throttle type, the idling rotatingspeed control can be performed by controlling the throttle valve openingdegree through feedback control (that is, the idling opening degree isnot determined using the idling adjusting screw used in the mechanicalthrottle device). Therefore, even if combustion products are graduallyaccumulated in the shaft supporting gap of the throttle valve shaft,decrease in the air flow rate (decrease in the idling rotating speed)caused by the accumulation of the combustion products can be compensatedby controlling the throttle valve opening degree. From this point ofview, the above-mentioned problem specific to the mechanical throttledevice (the problem of the decrease in idling rotating speed caused byaccumulation of combustion products in the shaft supporting gap) doesnot occur in the electronic control throttle device. In other words,there are differences in problem to be solved and in object between theair leak preventing material applied to the shaft supporting gap in theelectronic control throttle device and the air leak preventing materialapplied to the shaft supporting gap in the mechanical throttle device.

[0033] In an electronic control throttle device according to a furtheraspect of the invention, an electromagnetic shield member of a wire usedfor driving control of the electric drive actuator is a woven shieldcomposed of a tube-shaped member formed by weaving glass fiber and awoven thin metal wire member covering the tube-shaped member.

[0034] A conventional electromagnetic shield member of this kind isformed by covering a tube made of silicon rubber with a shielding outercover of woven thin metal wires. The electromagnetic shield member ofthe above-mentioned structure can substantially reduce its cost and caneffectively shield electromagnetic wave compared to the conventionalelectromagnetic shield member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIGS. 1A and 1B each is a perspective view showing a firstembodiment of an electronic control throttle device in accordance withthe present invention and a view explaining the principle.

[0036]FIG. 2 is an exploded perspective view showing a part of the firstembodiment of the electronic control throttle device.

[0037]FIG. 3 is a vertical cross-sectional view of the first embodiment.

[0038]FIG. 4 is a transverse cross-sectional view of the firstembodiment.

[0039]FIG. 5 is a front view of the first embodiment.

[0040]FIG. 6 is a rear view of the first embodiment.

[0041]FIG. 7 is an explanatory view showing a gear case detaching itscover, the gear case being provided in the throttle body of the firstembodiment.

[0042]FIGS. 8A and 8B each is an explanatory view showing the gear caseof FIG. 7 detaching part of the gears.

[0043]FIG. 9 is a view showing a one side of the throttle body of FIG.7.

[0044]FIG. 10 is an explanatory view showing a connector and throttlesensor case detaching its cover, the connector and throttle sensor casebeing provided in the throttle body of the first embodiment.

[0045]FIGS. 11A and 11B each is an explanatory view showing the processof connecting a motor terminal with a terminal connector used in theabove-mentioned embodiment.

[0046]FIG. 12 is a perspective view showing the terminal connector.

[0047]FIG. 13 is a cross-sectional view showing the motor case andconnecting terminal connector provided in the throttle body of the firstembodiment.

[0048]FIG. 14 is a vertical cross-sectional view showing a secondembodiment in accordance with the present invention.

[0049]FIG. 15 is a vertical cross-sectional view showing a thirdembodiment in accordance with the present invention.

[0050]FIG. 16A and 16B each is a perspective view showing an outline ofa fourth embodiment of an electronic control throttle device inaccordance with the present invention and a view explaining theprinciple.

[0051]FIG. 17 is a explanatory chart showing the relationship betweenovershoot occurring in the electronic control throttle and the minimumopening degree for the control purpose of the throttle valve.

[0052]FIG. 18 is a graph showing variations in air flow rate versusthrottle valve opening degree in a case where an air leakage preventingmember is applied along the whole circumference of the throttle valve inthe air flow passage of the electronic control throttle and in a casewhere the air leakage preventing member is applied and filled only inthe shaft support gap.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] Embodiments of the present invention will be described below,referring to the accompanied drawings.

[0054] Initially, the principle of an embodiment of an electroniccontrol throttle device with a default mechanism (a throttle device ofan internal combustion engine for a vehicle) in accordance with thepresent invention will be described below, referring to FIGS. 1A and 1B.FIG. 1A is a schematic perspective view showing an electric drivemechanism of throttle valve and a default mechanism in the presentembodiment, and FIG. 1B is an explanatory view equivalently expressingthe above-mentioned mechanisms.

[0055] Referring to FIGS. 1A and 1B, a flow rate of air flowing in anintake air passage 1 is adjusted corresponding to an opening degree of adisk-shaped throttle valve 2. The throttle valve 2 is fixed to athrottle valve shaft 3. In one end of the throttle valve shaft 3, afinal stage gear (referred to as a throttle gear) 43 of a gear mechanism(a reduction gear mechanism) 4 for transmitting power of a motor (anelectric drive actuator) 5 to the throttle valve shaft 3 is attached.The gear mechanism 4 is composed of a pinion gear 41 attached to themotor 5 and an intermediate gear 42 in addition to the throttle gear 43.The intermediate gear 42 is composed of a large diameter gear 42 aengaging with the pinion gear 41 and a small diameter gear 42 b engagingwith the throttle gear 43, and is rotatably inserted into a gear shaft70 fixed to a wall surface of a throttle body 100.

[0056] The motor 5 is driven corresponding to an accelerator signal inregard to a stepping amount of an accelerator pedal and a tractioncontrol signal, and the power of the motor is transmitted to thethrottle valve shaft 3 through the gears 41, 42, 43.

[0057] The throttle gear is a sectorial gear and fixed to the throttlevalve shaft 3, and also serves as a fixed side engaging element, to bedescribed later, in order to reduce number of parts, and has an engagingside 43 a for engaging with an arm portion 62 of an engaging lever (amoving side engaging element) 6 to be described later.

[0058] The engaging lever 6 is used for a default opening degree settingmechanism, and therefore, is hereinafter referred to as a default lever.The default lever 6 is idly inserted onto the throttle valve shaft 3 androtatable relative to the throttle valve shaft, and is an engagingelement in the moving side to the above-mentioned fixing side engagingelement (gear) 43. The fixing side engaging element (gear) 43 and themoving side engaging element (the default lever) 6 are attracted to eachother through a default spring 8 by connecting between a springfastening portion (shown by a reference character 64 in FIG. 2) of thedefault lever 6 and a spring fastening portion 9 fixed to the throttlevalve shaft 3 with the default spring 8.

[0059] A returning spring 7 is fixed to a spring fastening portion 10fixed to the throttle body 100 in one end, and the other end of a freeend side is hooked to a spring fastening portion 61 provided in thedefault lever 6 to act a force on the moving side engaging element (thedefault lever) 6 in a direction closing the throttle valve.

[0060] A full close stopper 12 is for determining a mechanical fullclose position of the throttle valve. When the throttle valve 2 isrotated toward a closing direction up to the mechanical full closeposition, one end of the stopper fixing element (herein, the throttlegear 43 also serving) fixed to the throttle valve shaft 3 is in contactwith the stopper 12 to block the throttle valve to be closed further. Astopper (sometimes called as a default stopper) 11 for setting a defaultopening degree is for keeping the opening degree of the throttle valve 2to a preset initial opening degree (a default opening degree) largerthan the mechanical full close position and the electrical full closeposition (a minimum opening degree on the control purpose) when anengine key is off (when the electric drive actuator is off). The springfastening portion 61 provided in the default lever 6 is in contact withthe default stopper 11 when the throttle valve is in the default openingdegree to block the throttle valve to rotate toward a directiondecreasing the opening degree of the default lever 6 (a closingdirection). The full close stopper 12 and the default stopper 11 areconstructed by adjustable screws (adjust screws) provided in thethrottle body 100.

[0061] By constructing as described above, the fixing side engagingelement (the throttle gear) 43 and the moving side engaging element (thedefault lever) 6 are set rotatable in being engaged together opposingagainst the force of the returning spring 7 within the range of openingdegrees above the default opening degree. The moving side engagingelement (the default lever) 6 is set to be blocked to move by thedefault stopper 11 and only the fixing side engaging element (thethrottle gear) 43 is set rotatable opposing against the force of thedefault spring 8 together with the throttle valve shaft 3 within therange of opening degrees below the default opening degree.

[0062] For example, in FIGS. 1A and 1B, the engine key is in off state,and in this state the default lever 6 is pushed back up to the positionin contact with the default stopper 11 by the force of the returningspring 7, and the throttle gear 43 and the throttle valve shaft 3 arekept to be engaged with the default lever 6 and are at a positioncorresponding to the default opening degree by receiving the force ofthe returning spring 7 through the arm portion of the default lever 6.Therefore, a preset gap is maintained between the throttle gear (thestopper stopping element) 43 and the full close stopper 12.

[0063] When the throttle valve shaft 3 is rotated from this state towardthe opening direction by the motor 5 through the gear mechanism 4, thethrottle gear 43 transmits power in the opening direction to the defaultlever 6 through an engaging chip 43 a and the arm portion 62 opposingagainst the force of the returning spring 7 to open the throttle valve 2up to a position where the power balances with the force of thereturning spring 7.

[0064] On the contrary, when the throttle valve shaft 3 is rotated fromthis state toward the closing direction by the motor 5 through the gearmechanism 4, the default lever 6 (the arm portion 61) follows therotation of the throttle gear 43 and the throttle valve shaft 3 untilthe default lever 6 is in contact with the default stopper 11. When thedefault lever 6 is in contact with the default stopper 11, only thethrottle gear 43 and the throttle valve shaft 3 are operated opposingagainst the force of the default spring 8 within the range below thedefault stopper 11 (the default opening degree) since the default lever6 is blocked to rotate in the closing direction below the defaultopening degree. The throttle gear (the stopper stopping element) 43 isbrought in contact with the full close stopper 12 at the mechanical fullclose position by driving the motor 5 only when the reference point onthe control purpose is checked, and accordingly the throttle gear 43 isnormally not brought in contact with the full close stopper 12.

[0065] In this default method, the spring force of the returning spring6 is effective only within the range above the default opening degreedue to existence of the default stopper 11. Therefore, since the springforce of the default spring 8 can be set within the range below thedefault opening degree without being affected by the spring force of thereturning spring 6, there is an advantage in that load of the defaultspring is made small and accordingly the torque required for theelectric drive actuator can be reduced and the electric load to theengine can be reduced.

[0066] In this embodiment, the returning spring 7 and the default spring8 are formed in coil-shaped torsion springs, and the diameter of thereturning spring 7 is made larger than the diameter of the defaultspring 8, and these springs 7, 8 are held around the shaft of thethrottle valve shaft 3 and placed between the throttle gear 43 and awall portion of the throttle body 100. By doing so, the default spring 8and the returning spring 7 are partly overlapped in a nearly coaxialcylinder shape (that is, a part of the default spring 8 is inserted intothe inside of the returning spring 7.)

[0067] In FIG. 1A, lengths of the arm portions 61, 62 of the defaultlever 6 and the arm of the stopping portion 9 are exaggeratively drawnfor convenience of drawing the figure, but actually the springs 7, 8 areused by a compressed state. Accordingly, the spring lengths in the axialdirection are short and correspondingly the arms are formed in shortprojecting chips (refer to the exploded equipment shown in FIG. 2).

[0068]FIG. 3 is a cross-sectional view in the axial direction of the airflow passage 1 of the electronic control throttle device in accordancewith the present invention, and FIG. 4 is a cross-sectional view in thedirection perpendicular to the axis of the air flow passage 1 of theelectronic control throttle device seeing from the upstream side.

[0069] As shown in these figures, a gear case 102 for containing thegear mechanism 4 is formed on one side wall of the throttle body 100integrally with the throttle body, and a bearing containing boss 101 forcontaining one of bearings 20 of the throttle valve shaft 3 is arrangedin projecting on an outer wall of the throttle body 100 inside the gearcase 102. The bearing 20 is sealed by a seal member 18 supported by aseal push 19. A spring (in this case, the returning spring) 7 out of thesprings 7, 8 arranged outside (having a larger diameter) is fixed to thespring fastening portion 10 (refer to FIG. 1, FIG. 2, FIG. 3) of thethrottle body 100 in one end 7 a, and a part of the spring in the sideof the one end 7 a is guided on the outer periphery of the boss 101.

[0070] In this embodiment, an annular groove 106 receiving a part of thereturning spring 7 is formed between the outer periphery of the bearingcontaining boss 101 in the side of the gear case 102 and the inner wallof the gear case 102. The bottom portion of the annular groove 106 isnot even in depth because of securing positions for attaching holes 150,as shown by the reference characters 106′, 106″ in FIG. 4. Therefore, aplurality of ribs 151 are arranged in the circumferential direction ofthe annular groove 106 so as to receive the returning spring 7 at aconstant level of depth of the annular groove 106. If the bottom portionof the annular groove 106 is even, the above-described ribs 151 can beeliminated and the returning spring 7 can be inserted a more deeperlevel of the annular groove 106.

[0071] The default lever (the moving side engaging element) 6 is a diskshape having the arms 61, 62, and one surface of the default leverreceives one end of the default spring 8 and the other surface in theopposite side receives one end of the default spring 8.

[0072] The default lever (the moving side engaging element) 6 iscomposed of a cylinder portion with bottom 6 a having an inner diameterslightly larger than an outer diameter of a spring 8 having a smallerdiameter out of the default spring 8 and the returning spring 7 and analligator portion 6 b formed in the peripheral edge of an opening of thecylinder portion with bottom 6 a, and a part of the spring 8 having asmaller diameter is inserted inside the cylinder portion with bottom 6 aand received by the bottom of the cylinder portion with bottom 6 a. Onthe other hand, a part of the spring 7 having a larger diameter isinserted on the outer periphery of the cylinder portion with bottom 6 aand received by one surface of the alligator portion 6 b.

[0073] The default lever 6 is joined with a sleeve 63 inserted on thethrottle valve shaft 3 in a unit, and holders (collars) of the defaultspring 8 is inserted on the outer periphery of the sleeve 63 between thethrottle gear 43 and the default lever 6.

[0074] That is, The default lever (the moving side engaging element) 6is placed between the wall portion of the throttle body 100 and the gear(the fixing side engaging element) 43, and the cylindrical collardivided into two members 14, 15 in the axial direction is placed betweenthe inner periphery of the default spring 8 between the default lever 6and the gear 43 and the outer periphery of the throttle valve shaft 3.

[0075] In a case where the collar is divided into the members 14, 15 asdescribed above, there is an advantage as described below compared to ina case of forming the collar with one collar member. That is, when thethrottle valve shaft 3 is rotated from the default opening degree towardthe full open direction opposing against the force of the default spring8, forces in directions opposite to each other are generated at the bothends of the default spring 8 caused by torsion. Therefore, when thecollar member to serve as the spring holder is formed in one member, alarge friction force caused by the torsion acts on the collar memberfrom the returning spring. As a result, the collar member may be wornand damaged. On the other hand, when the collar member is divided intothe members 14, 15 in the axial direction, the collar members 14, 15follow movement of each end portion of the default spring 8, and thecollar members do not receive an excessive force from the spring.Accordingly, the wear and damage described above can be prevented.

[0076] As shown in FIG. 2, the returning spring 7, the spring holder 13,the default lever 6, the collar member 14, the default spring 8, thecollar member 15, the throttle gear 43, the spring fastening member 9can be successively assembled through one end of the throttle valveshaft 3, and then the springs 7, 8 can be placed in compression statesby fastening the nut 17 through a washer 16.

[0077]FIG. 7 is a view showing the gear case 102 removing a gear cover103 and seeing from a direction shown by an arrow A of FIG. 3. Asdescribed above, the default spring 8 and the returning spring 7 arenearly coaxially arranged partially overlapping and displacing in theaxial direction around the throttle valve shaft 3. The diameter of thethrottle gear 43 is made larger than the outer diameter of the returningspring 7 placed outside out of the default and returning springs so thatthe returning spring does not interfere with the other parts, and thethrottle gear 43 and the smaller diameter gear 42 b of the intermediategear 4 are engaged with each other without difficulty.

[0078] The default stopper 11 and the full close stopper 12 are attachedon the side wall of the gear case in the throttle body 100.

[0079] Main effects in regard to the construction having been describedabove are as follows.

[0080] The returning spring 7 and the default spring 8 can beintensively arranged between the gear 43 provided in the throttle valveshaft 3 and the wall portion of the throttle body 100. Particularly, bythe structure that the returning spring 7 and the default spring 8 arearranged partially overlapping in the axial direction of the throttlevalve shaft (the structure of arranging the springs 7, 8 in parallel inthe radial direction), the arranging space in the longitudinal directionof the spring can be shortened (that is, the spring receiving structureof the default lever 6 makes a part of the returning spring 7 and a partof the default spring 8 overlapped in the axial direction), and further,the returning spring 7 is guided on the outer periphery of the bearingcontaining boss 101 for the throttle valve projecting toward the insideof the gear case 102 to use the outer periphery of the bearingcontaining boss 101 for the arranging space of the returning spring 7.In addition, the gear 43 also serves as the stopper stopping element.Therefore, the parts are substantially made intensive and rational bythe multiplier effect of the above to contribute to making the gear case10 and the whole throttle body 100 small in size, light in weight andsimplifying assembling the throttle body.

[0081] The motor case 110 integrated with the throttle body 100 has amotor inserting port 110 a opening to the inside of the gear case 102.

[0082]FIGS. 8A and 8B each is a view showing the inside of the gear case102 by removing the intermediate gear 42. In order to suppress vibrationof the motor more effectively than a conventional one in which the motorbracket is fastened at two points with screws, and to improve accuracyof positioning, the motor is designed as follows. That is, a contour ofthe motor bracket 5 a is nearly triangular, and three sides forming thecontour of the motor bracket are curved lines. The motor bracket 5 a isattached to the motor case by fastening to triangular point arrangedscrew holes provided a periphery of the motor inserting port 110 a withthree screws 160 in total, and motor positioning portions 130, 131, 132for positioning the motor by fitting to the three curved lines of themotor bracket 5 a to position the motor being formed in the gear case102. The inside of the motor positioning portions 130, 131, 132 hasnearly equal curvature to the above-mentioned three sides of the curvedlines of the motor bracket 5 a. Further, a part 70 a of the outerperiphery of a cylindrical portion 71 supporting the intermediate gearattaching shaft 70 also has a cut-off portion so as to trace a lineextending the curved line of the above-mentioned motor positioningportion 130. The cut-off line 3 a is also used as a part of curved linefor positioning the motor, and accordingly the motor can be placed nearthe gear mechanism 4 side by the distance to improve the partconfiguration.

[0083] A throttle sensor 30 for detecting throttle opening degree isattached to the other end of the throttle valve shaft 3 (an end in theside opposite to the gear mechanism 4 and the default opening degreesetting mechanism). The throttle sensor 30 is composed of a sensorhousing 31, a board 32 provided in the housing 31, a rotor 33, a brush34 provided in the rotor 33 and a cover 35, and the sensor housing 31having the board 32 is attached to the side wall of the throttle body100 with screws in a state of inserting on to one end of the throttlevalve shaft 3. On the other hand, the rotor having the brush 34 is fitto the throttle valve shaft 3 and fixed to the throttle valve shaft 3fastened with a nut 36 so as to rotate together with the throttle valveshaft 3. By sliding a printed resistor on a board 32 with the brush 34by rotation of the rotor 33, an opening degree signal of the throttlevalve is electrically output through a lead wire.

[0084] By providing the throttle sensor 30, a case 107 for containingthe throttle sensor 30 is formed on the side wall of the throttle body100 in the side opposite to the gear case 102. The case 107 also has acontaining space (a containing portion) 107 b for a connector 190 oflead wires (electric power supply wires) 205 to be connected to aterminal 51 (refer to FIG. 10, FIG. 11) in addition to a containingspace 107 a for the throttle sensor 30, and the sensor containing space107 a and the connector containing space 107 b are constructed in oneroom without boundary. Therefore, here, the case 107 is called as aconnector and throttle sensor case.

[0085] As shown in FIG. 4, the motor case 110 provided in the throttlebody 100 and the connector and throttle sensor case 107 are arranged soas to intersect each other at right angle, and a motor terminalextracting port 180 is formed in the side of the bottom portion 110 b ofthe motor case 110, and the containing space 107 b for the connector 190is formed adjacent to the side of the bottom portion 110 b of the motorcase. By forming the sensor containing space 107 a and the connectorcontaining space 107 b as one room, as shown in FIG. 10 (FIG. 10 is aview showing the throttle sensor case 107 of the throttle body 100removing the case cover 37 and seeing from the direction shown by anarrow B of FIG. 3), the wire lead portion 30 a of the throttle sensor 30is arranged so as to directed to the motor terminal connector containingspace 107 b.

[0086] The throttle sensor 30 has two sensor detecting portions of sametype in order to back up the sensor when one of the sensor detectingportions produces trouble, and accordingly there are two set of thewires 204 extracted from the sensor 30.

[0087] As shown in FIGS. 5, 6, and 9, the connector and throttle sensorcase 107 is covered with a cover 37, and a wiring guide 123 forgathering and guiding the electric power supply wires 205 to beconnected to a connector and the lead wires 204 of the throttle sensor30 is fit into a groove 122 provided on the wall portion of theconnector and throttle sensor case 107 to be attached with the cover 37.The wiring guide 123 is formed of a rubber plate, and has a plurality ofguide holes 124 used for penetrations of the electric power supply wires205 and the sensor lead wires 204.

[0088] Since the wiring extracting portion 30 a of the throttle sensor30 is placed directing to the motor terminal connector containing space107 b as described above, the wires 204 led from the terminal of thethrottle sensor 30 and the wires 205 led from the motor terminal 51through the connector 190 can be merged at adjacent positions in thebeginning in the one room, and accordingly these wires can be gatheredwithout difficulty and can be extracted out of the throttle body.Therefore, this construction is useful to simplify the wiring work andthe part assembling work.

[0089] In order to reduce manufacturing cost, an electromagnetic shieldmember 206 of the wires 204, 205 is a woven shield composed of atube-shaped member formed by weaving glass fiber and a woven thin metalwire member covering the tube-shaped member.

[0090] The motor terminal extracting port 180 provided in the bottomportion of the motor case 110 is exposed to the connector containingportion (the containing space) 107 b, and the guide 155 for guiding theconnector to the motor terminal extracting port 180 when the connectoris plugged to the motor terminal 51 is formed on the inner wall surfaceof the containing portion 107 b of the motor terminal connector 190.(refer to FIG. 10, FIG. 13. FIG. 10 is a view showing the inside of theconnector and throttle sensor case 107 detaching the motor terminalconnector 190 and seeing from the side of the case opening. FIG. 13 is aC-C line cross-sectional view showing the motor terminal connector undera connecting process being taking on the plane of the line C-C of FIG.10.)

[0091] The guide 155 is formed at mold forming of the throttle body 100at the same time, and composed of a pair of opposite wall surfacesformed in such a shape that the width is wide in the receiving side ofthe connector and gradually narrowed toward the motor terminalextracting port 180.

[0092]FIG. 11 is a cross-sectional view showing the inner structure ofthe motor case 110 and the connector and throttle sensor case 107 seeingby changing the view angle from FIG. 13. FIG. 11A shows a state halfwaythrough the process of plugging the connector, and FIG. 11B shows astate after plugging the connector 190 to the motor terminal 51.

[0093] The connector 190 can be easily connected to the motor terminal51 without difficulty of positioning the connector 190 to the motorterminal 51 because by containing the motor 5 in the motor case 110 themotor terminal 51 can be seen in the connector containing space 107 bthrough the terminal extracting port 180, and in this state the motorterminal connector 190 is inserted from the terminal containing portion107 b using the guide 155. Even if the motor terminal 51 is,particularly, placed in a deep position of the connector containingportion 107 b and behind the other parts, the connector can be insertedby being guided by the above-mentioned guide 155 without difficultywhile being positioned.

[0094] As shown in FIGS. 4, 11A, 11B and 12, the motor terminalconnector 190 is a plastic molded member of a socket type, and a pair ofmetal chips 191 for terminal connector is embedded in the motor terminalconnector. In this embodiment, the portion 190 a embedding the metalchips 191 is formed in a nearly rectangular shape and a portionfollowing to the portion 190 a is formed in a plate with reinforcing rib192 to rationalize use of material. The connector 190 is guided to theterminal extracting port 108 placed at a deep position through a narrowportion. Therefore, in order to make the plugging work easy, the lengthfrom the motor terminal extracting port 108 to a position near theopening of the connector and throttle sensor case 107 is shortened.

[0095] As shown in FIGS. 5, 6 and 9, a belt-shaped metal member 208 forholding the plurality of connectors 201 to 203 is welded on an outersurface of the cover 37 of the connector and throttle sensor case 107.By attaching the plurality of connectors 201 to 203 to the belt-shapedmetal member 208 based on a predetermined layout, wire connecting workcan be easily performed without trouble of the layout configuration ofthe connector parts at assembling at the manufacturing location. Thereference character 250 of FIG. 3 indicates an engine cooling waterinlet pipe.

[0096] The coil-shaped torsion spring is used for the returning spring 7and the default spring 8 in this embodiment, but it is not limited tothe coil-shaped torsion spring. For example, a belt-shaped coil springmay be used. An embodiment of FIG. 15 employs a belt-shaped coil springfor the default spring 8, but the other structure is the same as that ofthe first embodiment. According to this type, the inside of the gearcase can be made smaller.

[0097] An embodiment of FIG. 14 eliminates the collar members 14, 15,but the other structure is the same as that of the first embodiment.

[0098] In an embodiment of FIGS. 16A and 16B, contrary to theabove-mentioned embodiments, the returning spring 7 is placed outsidethe default spring 8.

[0099] The principle of the electronic control throttle device of FIGS.16A and 16B is as follows.

[0100] In this embodiment, the gear (the fixing side engaging element)43 fixed to the throttle valve shaft 3 and the default lever 6 idlyinserted onto the throttle valve shaft 3 and rotatable relative to thethrottle valve shaft are connected with the returning spring 7 so as toattract each other. this connection can be performed by fastening oneend of the returning spring 7 to the default lever 6 and the other endof the returning spring 7 to a spring fastening portion 9 of thethrottle valve shaft 3.

[0101] On the other hand, the default spring 8 acts a force on thedefault lever 6 in a direction to open the throttle valve by fasteningone end 8 a of the default spring 8 to a spring fastening portion 10provided in the throttle body 100 and the other end 8 b to a springfastening portion 61 of the default lever 6.

[0102] By constructing as described above, the gear (the fixing sideengaging element) 43 and the default lever (the moving side engagingelement) 6 are rotatable in being engaged together opposing against theforce of the default spring 8 within the range of opening degrees belowthe default opening degree. The default lever 6 is blocked to move bythe default opening degree setting stopper 11′ and only the throttlegear 43 becomes rotatable opposing against the force of the returningspring 7 together with the throttle valve shaft 3 within the range ofopening degrees above the default opening degree. In this embodiment,the diameter of the default spring 8 is larger than the diameter of thereturning spring 7, and the springs are arranged around the shaft of thethrottle valve shaft 3 so that the default spring 8 is outside and thereturning spring 7 is inside.

[0103] Although arrangement of the springs 7, 8 in this embodiment isreverse to the arrangement in the first embodiment, arrangement of theother parts is the same as that in the above-described embodiments. Bydoing so, the same effect as that of the first embodiment can beattained.

[0104] In each of the embodiment of the electronic control throttledevice, the gap (the shaft supporting gap) between the throttle valveshaft 3 and the shaft inserting through hole 181 for guiding thethrottle valve shaft 3 to the bearing 20 provided in the wall portion ofa throttle body is filled with an air leak preventing material. The airleak preventing material, for example, a dryable liquid lubricant suchas molybdenum disulfide (MOS₂) is applied from downstream side of thethrottle valve 2 onto the limited areas of gap between the throttlevalve shaft 3 and the shaft inserting through holes 181 and thesurrounding such as the diagonally shaded areas shown by the referencecharacter 310 in FIG. 6, and penetrates and fills the shaft supportinggap. By filling the shaft supporting gaps with the air leak preventingmaterial, since the intake air flow rate (the leak air flow rate)supplied to the internal combustion engine through the shaft supportinggap of the throttle valve shaft can be eliminated, the minimum openingdegree on the control purpose of the throttle valve can be increasedlarger than in the conventional one by that amount. In the presentinvention, by making use of this fact the minimum opening degree on thecontrol purpose is set a value lager than the overshoot of the throttlevalve when opening degree of the throttle valve is changed from themaximum opening degree on control purpose of the throttle valve to theminimum opening degree. The operation and effects are as described inthe section SUMMARY OF THE INVENTION. That is, by applying the air leakpreventing material (for example, molybdenum disulfide), as shown inFIG. 17, since the minimum opening degree on the control purpose can beset a value lager than the mechanical full close position byapproximately 2° (in a conventional case, a value lager than themechanical full close position by approximately 1°) , the minimumopening degree on the control purpose can be increased higher by a valuecorresponding to the overshoot (for instance, approximately 1.5°) whenopening degree of the throttle valve is changed from the maximum openingdegree on control purpose (the electrical full open position) to theminimum opening degree (the electrical full close position) as shown bythe line {circle over (2)}. Therefore, the stopper blocking element inthe side of the throttle valve can be prevented from hitting on thestopper (the full close stopper) determining the mechanical full closeposition even if the overshoot occurs. Accordingly, even if theovershoot occurs, it is possible to prevent over current from flowing inthe motor.

[0105] Further, by applying the air leak preventing material to theshaft supporting gaps and the surrounding, the following operation andeffect can be obtained.

[0106] That is, in a case of performing idling rotating speed controlusing the electronic control throttle device, in addition to the normalengine rotating speed feedback control there is a state of open controlin order to cope with inrush load such as operation of an airconditioner. Further, in a gasoline engine directly injecting fuel intothe engine (DI-G engine), since the required air flow rate is increasedduring stratified combustion (ultra-lean burn) regardless of the enginerotating speed (A/F=40:1), there is a state of open control. Therefore,it is necessary to improve accuracy of air flow rate to throttle openingdegree (particularly, accuracy near 1 to 7°).

[0107] However, when the air leak preventing material is applied ontothe air passage wall along the whole circumference of the throttlevalve, accuracy of air flow rate, particularly, accuracy in a lowopening degree range has been low due to deviations in applyingthickness and concentration of the air leak preventing material.

[0108] On the other hand, when the air leak preventing material is notapplied onto most part of the circumference of the throttle valve bylimiting the applying area of the air leak preventing material only tothe shaft support gap and the surrounding, the cause of the deviationscan be eliminated and the accuracy of air flow rate can be improved. Asan experimental result verifying the above-mentioned effect, FIG. 18 isa graph showing variations in air flow rate versus throttle valveopening degree in a case where an air leakage preventing member isapplied along the whole circumference of the throttle valve in the airflow passage of the electronic control throttle and in a case where theair leakage preventing member is applied and filled only in the shaftsupport gap.

[0109] According to the present invention, an electronic controlthrottle device having an electric drive actuator, a gear mechanism, adefault opening degree setting mechanism can be made small in size,light in weight and simple in assembling and wire harness.

[0110] Further, reliability of the electronic control throttle devicecan be improved by preventing the throttle valve from hitting on astopper at the mechanical full close position even if an overshootspecific to the electronic control throttle device occurs when thethrottle valve rapidly changes from the maximum opening degree on thecontrol purpose to the minimum opening degree.

What is claimed is:
 1. A throttle device for an internal combustionengine comprising an electric drive actuator for opening and closing athrottle valve to control an intake air flow rate of the internalcombustion engine, and a default opening degree setting mechanism forkeeping an opening degree of said throttle valve at a preset openingdegree (hereinafter, the preset opening degree is defined as a defaultopening degree) larger than a full close position when said electricdrive actuator is not energized, wherein a gear case for containing agear mechanism to transmit power of said electric drive actuator to athrottle valve shaft is arranged on an outer wall of a throttle body,and a returning spring for acting a spring force on said throttle valvein a closing direction and a spring (hereinafter, referred to as adefault spring) for acting a spring force on said throttle valve in adirection toward a side of the default opening degree seeing from thefull close position of the throttle valve have diameters different fromeach other, both of said springs being held around a shaft of saidthrottle valve shaft and arranged between a gear attached to saidthrottle valve shaft in said gear mechanism and a wall portion of thethrottle body.
 2. A throttle device for an internal combustion engineaccording to claim 1 , wherein at least a part of one spring among saidreturning spring and said default spring having a smaller diameter isinserted inside the other spring having a larger diameter, and thespring having the larger diameter is placed in being guided by an outerperiphery of a bearing containing boss for the throttle valve shaftprojecting inward of said gear case in a manner that one end of thespring having the larger diameter is fixed to the wall portion of thethrottle body.
 3. A throttle device for an internal combustion engineaccording to any one of claim 1 and claim 2 , wherein a diameter of afinal stage gear provided in said throttle valve shaft is larger than anouter diameter of a spring having a larger outer diameter out of saidreturning spring and said default spring, and said final stage gear isengaged with an intermediate gear.
 4. A throttle device for an internalcombustion engine according to any one of claim 1 to claim 3 , whichcomprises an engaging element (hereinafter, referred to as a fixing sideengaging element) fixed to said throttle valve shaft, and an engagingelement (hereinafter, referred to as a moving side engaging element)idly inserted onto said throttle valve shaft and rotatable relative tosaid throttle valve shaft, wherein said default spring connects betweena spring fastening portion of said moving side engaging element and aspring fastening portion of said throttle valve shaft so that saidfixing side engaging element and said moving side engaging elementattract each other, said returning spring acting a force on said movingside engaging element in the direction closing the throttle valve, saidfixing side engaging element and said moving side engaging element beingengaged and rotatable together opposing against a force of saidreturning spring within a range of opening degrees larger than thedefault opening degree, only said fixed side engaging element being setrotatable together with the throttle valve shaft opposing against aforce of said default spring by blocking movement of said moving sideengaging element by a default opening degree setting stopper within arange of opening degrees smaller than the default opening degree, saidreturning spring and said default spring being arranged around the shaftof said throttle valve shaft so that said returning spring is placedoutside and said default spring is placed inside.
 5. A throttle devicefor an internal combustion engine according to any one of claim 1 toclaim 3 , which comprises a fixing side engaging element fixed to saidthrottle valve shaft and a moving side engaging element idly insertedonto said throttle valve shaft and rotatable relative to said throttlevalve shaft, wherein said returning spring connects between a springfastening portion of said moving side engaging element and a springfastening portion of said throttle valve shaft so that said fixing sideengaging element and said moving side engaging element attract eachother, said default spring acting a force on said moving side engagingelement in the direction opening the throttle valve, said fixing sideengaging element and said moving side engaging element being engaged androtatable together opposing against a force of said default springwithin a range of opening degrees larger than the default openingdegree, only said fixed side engaging element being set rotatabletogether with the throttle valve shaft opposing against a force of saidreturning spring by blocking movement of said moving side engagingelement by a default opening degree setting stopper within a range ofopening degrees smaller than the default opening degree, said returningspring and said default spring being arranged around the shaft of saidthrottle valve shaft so that said default spring is placed outside andsaid returning spring is placed inside.
 6. A throttle device for aninternal combustion engine according to any one of claim 4 and claim 5 ,wherein said moving side engaging element is placed between the wallportion of said throttle body and said fixing side engaging element, anda cylindrical collar member divided into two portions in an axialdirection is placed between an inner periphery of a spring out of saiddefault spring and said returning spring placed between said moving sideengaging element and said fixing side engaging element and an outerperiphery of said throttle valve shaft.
 7. A throttle device for aninternal combustion engine according to any one of claim 4 to claim 6 ,wherein the gear attached to said throttle valve shaft in said gearmechanism also serves as said fixing side engaging element.
 8. Athrottle device for an internal combustion engine according to any oneof claim 4 to claim 7 , wherein said moving side engaging element iscomposed of a cylinder portion with bottom having an inner diameterlarger than an outer diameter of one spring out of said default springand said returning spring having a smaller diameter and an alligatorportion formed in an opening periphery of said cylinder portion withbottom, and a part of the other spring having a larger diameter isinserted on an outer periphery of said cylinder portion with bottom andsupported with a surface of said alligator portion.
 9. A throttle devicefor an internal combustion engine comprising an electric drive actuatorfor opening and closing a throttle valve to control an intake air flowrate of the internal combustion engine, wherein a throttle body, a motorcase containing a motor composing an electric drive actuator and acontaining portion of a connector connecting by plugging to a motorterminal provided in an end plate of said motor are formed in a unit,and a motor terminal extracting port for exposing said motor terminal tosaid containing portion of the connector is formed on a bottom portionof said motor case, and a guide for guiding said connector to said motorterminal extracting port when said connector is plugged to said motorterminal is formed on an inner wall surface of said containing portionof the connector.
 10. A throttle device for an internal combustionengine comprising an electric drive actuator for opening and closing athrottle valve to control an intake air flow rate of the internalcombustion engine, a motor case for containing a motor composing saidelectric drive actuator being integrated with a throttle body in a unit,wherein in said throttle body, a motor terminal extracting port isformed in a side of a bottom portion of said motor case, a containingspace of a connector to be connected to the motor terminal being formedadjacent to the side of the bottom portion of said motor case, thecontaining space of the connector and a containing space for containinga throttle sensor provided at one end of a throttle valve shaft beingformed in one room, a wire lead portion of said throttle sensor beingarranged in being directed to said containing space of the motorterminal connector.
 11. A throttle device for an internal combustionengine according to claim 10 , wherein a connector and throttle sensorcase which forms said containing space of the motor terminal connectorand said containing space for containing the throttle sensor in one roomis covered with a cover, and a wiring guide for gathering electric powerwires to be connected to said connector and lead wires of said throttlesensor to one position to pass therethrough is inserted into a grooveprovided on a wall portion of said connector and throttle sensor case tobe attached with said cover.
 12. A throttle device for an internalcombustion engine according to claim 11 , wherein a belt-shaped metalmember for holding a plurality of connectors is welded on an outersurface of said cover.
 13. A throttle device for an internal combustionengine comprising an electric drive actuator for opening and closing athrottle valve to control an intake air flow rate of the internalcombustion engine, a motor case for containing a motor composing saidelectric drive actuator and a gear case for containing a gear mechanismto transmit power of said motor to a throttle valve shaft beingintegrated in a unit, wherein a motor inserting port of said motor caseis opened to said gear case, said motor being attached to said motorcase by fastening a motor bracket to triangular point arranged screwholes provided a periphery of said motor inserting port with threescrews in total, three sides forming a contour of said motor bracketbeing curved lines, a motor positioning portion fitting to the threecurved lines of said motor bracket to position the motor being formed insaid gear case.
 14. A throttle device for an internal combustion enginecomprising an electric drive actuator for opening and closing a throttlevalve based on a signal controlling an intake air flow rate of theinternal combustion engine, wherein a gap between a throttle valve shaftand a shaft inserting through hole for guiding said throttle valve shaftto a bearing provided in a wall portion of a throttle body is filledwith an air leak preventing material, and a minimum opening degree oncontrol purpose of said throttle valve is set to a value larger than anamount of overshoot of said throttle valve occurring when opening degreeof said throttle valve is changed from a maximum opening degree oncontrol purpose of said throttle valve to the minimum opening degree.15. A throttle device for an internal combustion engine comprising anelectric drive actuator for opening and closing a throttle valve basedon a signal controlling an intake air flow rate of the internalcombustion engine, wherein a gap between a throttle valve shaft drivento open and close the throttle valve by said electric drive actuator anda shaft inserting through hole for guiding said throttle valve shaft toa bearing provided in a wall portion of a throttle body is filled withan air leak preventing material.
 16. A throttle device for an internalcombustion engine comprising an electric drive actuator for opening andclosing a throttle valve based on a signal controlling an intake airflow rate of the internal combustion engine, wherein a minimum openingdegree on control purpose of said throttle valve is set to such a valuethat said throttle valve does not hit to a full close stopper by anovershoot of said throttle valve occurring when said throttle valve ischanged from a maximum opening degree on control purpose of saidthrottle valve to the minimum opening degree.
 17. A throttle device foran internal combustion engine according to any one of claim 14 and claim15 , wherein said air leak preventing material is molybdenum disulfide,and applied onto portions limited to between said throttle valve shaftand said shaft inserting through hole and the surrounding among portionsaround an outer periphery of said throttle valve.
 18. A throttle devicefor an internal combustion engine comprising an electric drive actuatorfor opening and closing a throttle valve to control an intake air flowrate of an internal combustion engine, wherein an electromagnetic shieldmember of a wire used for driving control of the electric drive actuatoris a woven shield composed of a tube-shaped member formed by weavingglass fiber and a woven thin metal wire member covering the tube-shapedmember.